This invention relates to flow modulating valves for controlling pressurized hydraulic fluid flow to hydraulic motors, and more particularly to such valves as used in systems for driving pumps, such as liquid fuel pumps of centrifugal design.
There is need in such systems, and other systems, for valves of simple, rugged design, and wherein metal-to-metal engagement of valve elements is minimized or eliminated. Conventional spool valves do not serve these purposes in the simple, efficient manner now enabled by the present valve. Typically, such prior valves are cylindrical lapped and honed spool and sleeve assemblies wherein close tolerance end pieces control the flow by changing the flow through a radial hole. The exposed area of the hole is a function of the axial position of the sleeve. These devices require very close fitted parts (on the order of 50 millionths of an inch) and cannot control a large flow without a significant pressure drop, say on the order of 500 to 1000 psi for 25 gpm.
There is also need for improved centrifugal pumps driven by hydraulic motors, as for example are controlled by such flow modulating valves for use in fuel pumping systems.